1. Field of the Invention
This invention relates to a communication system and, more particularly, to a transceiver that avoids imparting jitter to data transmitted by the transceiver when the transceiver receives data-dependent jitter. The transceiver transmits substantially jitter-free transition edges of the data by constructing a single edge during culmination of a consistent bit pattern within the received data and multiplying the single edge by however many clock cycles are needed to maintain a jitter-free clocking reference for the transmitted data.
2. Description of the Related Art
A communication system is generally well-known as containing at least two nodes interconnected by a communication link. Each node may include both a transmitter and a receiver, generally referred to as a “transceiver.” The transceiver provides an interface between signals sent over a communication link and a digital system which operates upon that signal in the digital domain.
It is generally desirable that the communication link accommodate not only digital data, but also various forms of digital data such as audio data, video data, or bursts of data typically derived from a computer domain. The communication link can either be wire-based or wireless. The wired communication link can either be formed of copper or a waveguide of optical fiber.
The digital signals forwarded across the communication system are generally sent from a source to a destination. The source, similar to the destination, is a digital system and, preferably, can be classified as a multimedia device. A multimedia device can include a telephone, a compact disc (CD) player, a digital video disc (DVD) player, a computer, an amplifier, a speaker, or any device which can send and receive different types of data across the transmission line of the network.
Popular types of data include streaming data or packetized data. Streaming data is data that has a temporal relationship between samples produced from the source onto the communication system. The relationship between those samples must be maintained across the communication link to prevent perceptible errors, such as gaps or altered frequencies. A loss in the temporal relationship can cause a receiver at the destination to present jitter, echo or, in the worst instance, periodic blanks in the voice or video stream. Converse to streaming data, packetized data is data which need not maintain the sample rate or temporal relationship of that data and, instead, can be sent as disjointed bursts across the communication link.
Data transmitted across a communication link is generally encoded and placed within a packet or frame. There are numerous encoding schemes currently being used. A popular code includes either a bi-phase code or a, Miller code. The bi-phase code requires that for each logic high value of source data, a transition occurs at the middle as well as boundary regions of that clock phase. In Miller coding, a logic high value is encoded by transitioning at the center or middle of the clock phase, but not at the boundary regions of the clock phase. While Miller coding avoids encoding data at twice the source data rate, Miller coding unfortunately presents an accumulated DC value, the significance of which is set out in the commonly assigned patent application Ser. No. 09/710,220 entitled “Encoder within a Communication System that Avoids Encoded DC Accumulation and can use Coding Violations to Synchronize a Decoder and Detect Transmission Errors,” herein incorporated by reference.
Regardless of the coding technique used, a clock is needed to synchronize with and thereby sample transitions of the streaming or non-streaming data sent across the communication link. In most instances, the master clock used to generate the data originates from the source, whereupon the data is synchronized to the master clock when it is received by a node downstream of the source. Digital systems within the downstream node or nodes often employ various clock recovery techniques to recoup a clock from the data received by that node. Ideally, the recovered clock should transition at a regular and periodic rate, consistent with the master clock of the source node. Unfortunately, however, due in part to the band-limited transmission networks and/or the low-pass characteristics of detectors within one or more nodes, jitter is imparted upon the data as received by the various nodes. If slave clocks are to be accurately recovered, and which substantially mimic the master clock, a technique must be derived that can avoid recovering any jitter induced onto the data stream. This means that if transition rates change depending on whether the encoder encodes a logic 1 or a logic 0 voltage value, that change should not cause downstream jitter recovery problems. A circuit, system, and method is thereby needed which can recover and/or generate a local slave clock absent any data-dependent jitter produced by the band-limited transmission links. Avoiding jitter on the recovered clock not only provides a more accurate synchronous operation of digital subsystems in each nodes, but also prevents compounding the jitter from one node to the next, downstream node.